The problem with calling a Soros donation "foreign money"

Today on his radio program, Rush Limbaugh reacted to the news of George Soros' $1 million donation[1] to Media Matters thusly: "You want to talk a little foreign money in politics? George Soros has admitted to donating $1 million to Media Matters for America."

I hesitate to point this out, since Rush Limbaugh is typically so careful with his facts, but George Soros[2] is a U.S. citizen. He can vote and everything.